Thursday, January 23, 2014

Update - I've extended the table of temperature extremes below
Tennis fans everywhere will know that we had a pretty torrid heat wave last week, the first week of the Australian Open. It wasn't our hottest, but it went for four days. In Melbourne max temperatures were were 42.8,41.7, 43.9 and 43.9°C, or, if you prefer,109, 107, 111, 111°F. This forecast from the BoM explains what was happening; it happened as predicted, a bit warmer at the end. MikeH in comments noted this more complete report from B0M.

There's the usual argument about AGW. WUWT doesn't think so. In fact, they won't much concede that it was hot, and say it happens all the time here. So I thought I'd review in this post our summer temperature history, and also refute some notions that it's all happened before but been hushed up by "adjustments".

Data

The Bureau of Meteorology here has online daily data which is unadjusted. It's convenient to use, but not to download. For that I used GHCN Daily files which can be found here. They are unadjusted historic temperatures, derived from (and apparently identical to) BoM. Melbourne’s file is ASN00086071.dly; it has good coverage from June 1855 to Dec 2013. I supplemented it with current online data to date.. I extracted them to a CSV file which I've placed here.

Plots

I've plotted each summer (DJF) max temperatures from 1856 to 2014 (counting by the JF year).

1860
1870
1880
1890
1900
1910
1920
1930

1940
1950
1960
1970
1980
1990
2000
2010

You can switch from year to year using the top buttons, and go to any decade year with the radio buttons.

Our summers are made up of many pleasant days, with southerly winds, with heat when the wind blows from the North. Notably hot summers were in 1908, 1939, 1983, 2009. The last three had devastating wildfires on the hottest days, which I've linked. Big heat has bad consequences here. We lose towns, homes and people.

Table of extreme temperatures

Originally, I had here a list of the twenty hottest days in Melbourne since 1855. Following a suggestion in comments by SC M, I have updated to inclide tables of the 20 highest daily max, highest min, lowest max and lowest min. I've marked those occurring in the last five years in red. For highest max, there are seven. Click the buttons.

High Max Low Max High Min Low Min

Adjustments?

In the WUWT thread I encountered over and over claims that BoM had rigged the records by adjusting old readings downwards. It's very hard to get specifics (typically the complainant just gives a link, which is often to a rant about GHCN, or GISS). Eventually it crystallised to complaints about Acorn. This is a recent homogenised set of data for 112 chosen stations, starting in 1910. The lead post in fact claimed that the BoM had discarded all data before 1910, which puzzled me.

But of course the data is not discarded. All the old unadjusted data is available from BoM, and also from GHCN. And it is what the BoM uses when talking about station extreme temperatures. If you go to the Melbourne climate page, for example, it will tell you that the hottest December day was 15 December 1876. That's not Acorn.

So how do we know these are really unadjusted? I've known since boyhood that Melb reached 114.1°F on Jan 13, 1939. That's what the record still says. But I checked others. The National Library has an old Melb (and others) newspapers here. I've checked a few of the reportewd high temps; the GHCN record linked here agrees with the contemporary reports. I think it's up to claimants of adjustment to give one example from this dataset.

From the BOM "Special Climate Statement 48 – one of southeast Australia’s most significant heatwaves"

"The heatwave was more notable **for persistent heat than for individual extreme hot days**, but some locations still had their hottest day on record, particularly in the southeast of South Australia, and around and to the west of the Snowy Mountains in New South Wales."

"The daily mean temperature of 35.45°C on the 16th was Melbourne’s highest on record, just surpassing the 35.4°C observed on 30 January 2009. All four instances of daily mean temperature of 35°C or above in Melbourne have occurred since 2009, two in 2009 and two in 2014. "http://www.bom.gov.au/climate/current/statements/scs48.pdf

Nike should know that he is talking about temperature extremes when he is discussing heat waves.There cause and exceptional nature are not necessarily driven by the same physical phenomenonas those that drive the mean summer time temperatures.

This recent heat wave was exceptional compared to past events, however, the factorsthat produce these terrible events are dependent on a chance combination of phenomenonthat is relatively rare.

Extended heat waves in the South and South-Eastern parts of Australia require a numberof things to occur simultaneously.

[Note: the following is only a suggested sequence of events and it is not to be treated as a definitive explanation of what happens in any given heat-wave.]

1. The heat wave is usually proceeded by a build up of heat in Australia' central deserts. This could be bought about by an extended dry period in central Australia - usually leading to a slow build of heat. Alternatively, the heat could quickly build up in the southern deserts because of a powerful rain event(*) along the inter-tropical convergence zone that lingers along Australia's north and western coasts during the Southern summer. The rising air from this tropical rain event moves high up into the upper troposphere before moving towards the south and east. It then descends onto the Southern and South Eastern parts of Australia producing a building high pressure dome of extremely dry and hot compressing air that provides the heat for the coming heat-wave.

(*) Not this could be due a rapid onset the Monsoon or even a large than normal Madden-Julian Oscillation event in far-northern Australia.

2. A large blocking high in the South Tasman. This is usually formed by the reinforcement of the semi-permanent high that is located in the southern Tasman Sea. During the Summer months High pressure systems move from west to east at latitudes that can (on occasion) reach as far south as Southern Tasmania.

3. The blocking high in the Southern Tasman determines the way in which the building heat in Australia's southern deserts is vented off the Australia continent and into the surrounding oceans. With the blocking high firmly ensconced in the Southern Tasman, this means that building heat in the central and southern deserts is pushed south over the states of South Australia and Victoria [which contain the large cities of Adelaide and Melbourne].

4. And last but not least, the presence of a sharp cold front that extends diagonally from the about + 25 - 30 degrees south on the Western Australia coast all the way down deep into the Southern Ocean below South Australia. This cold front is slowly moving towards the east. As it moves, it acts like a large diagonal brick wall of cold dense air, that diverts the southerly moving high temperature air coming off the deserts, funneling the super-heated air towards the southern state capitals of Adelaide and Melbourne.

5. Of course, the whole shebang is helped if the summer time maximum's in Southern and South-Eastern Australia are higher than normal.

[Note: You do not need all of these ingredients to get a heat wave but at least a couple of these phenomenon have to occur to get the whole show on the road.]

"Nike should know that he is talking about temperature extremes when he is discussing heat waves. There cause and exceptional nature are not necessarily driven by the same physical phenomenon as those that drive the mean summer time temperatures."

Yes, heat waves are not climate. It seems we've always had them. But there is some indication of a pattern that the very hot days are getting hotter. That's why I drew attention to the 7/20 hottest days in the last five years. It's not proof, and more evidence is needed to affirm the pattern.

Anonymous (Mike H), You cannot be serious, can you? The selection of dates "......from 1951-2008......" covers a period from the bottom of a cooling period [1945 - 1975] to the peak of a warming period [1975 - 2005]. This is cherry picking of dates at its finest. Why have you left out the earlier dates? Could it be because they do not support your case?

Sounds like a reasonable idea Nick - However, all it proves is that temperatures havebeen going up over the last few hundred 100 years and no one disputes this. In addition,it says nothing about what is causing that increase.

I would be interested to see a similar 20 hottest list for overnight minimum temperatures. I recall somewhere that minima are more strongly affected by AGW than maxima - though data for one location can't hope to be definitive of course.

SCM,Yes. I can do that. My current project is preparing similar graphics for a number of cities and sites around the world. The graphic would show daily max and min. I can collect top 20 hot max, cold max, hot min, cold min.

FWIW four consecutive daily maxima over 40 is without precedent and one year 2013 1014 has that. Very few decades have four days over 40 daily maxima, and none consecutively. This year WAS a record breaker.

I've done something similar for Adelaide http://s5.postimg.org/o8fr2snvr/adel_summer_temp.jpgThe older temperatures were in park land site that was closed in 1979. The modern site has setting sun reflecting on the Stevenson Screen in a built up location.

The old Melbourne observations were taken in the botanic gardens (shifted prior to the shrine of remembrance being built).

I came up with a way of comparing heat waves more easily. Rather than adding up the degrees over a certain temperature, I added together the squared of the degrees above 32°C (F). You might not agree with it but it weights the hot days as 22 days of 35°C is the same as 2 days at 44°C and one day at 46°C.

Its not up to date but here are the the plots for Adelaide http://s5.postimg.org/ayr81jt2f/Total_F_Adelaide.pngand Melbourne. http://s5.postimg.org/i4nkhqrjb/F_Melbourne.png. It has not been updated in the past two weeks.

Carrick,There's a more detailed (spherical) picture here. Yes, in Australia the heat was mainly in the SE (plus W NSW and Qld). There were complaints about heat in SE Brazil and Argentina, which show up on the map.

As for US, the East of course was very cold. In anomaly terms, Alaska was very warm, and the West quite warm too.

Elsewhere, N Siberia was cold; Central Asia and Europe quite warm.

As for Australia's geography, a lot of our warmth in the last 18 months seems to be due to warm surrounding seas. I believe this heat wave was due to a puff of warm air from the Indian Ocean NW of WA. The phenomenon may be related to recent claims that trade winds in the Pacific have strengthened, causing a cool E Pafific and global "pause". That would blow the heat our way.